Not Applicable
1. Field of the Invention
The present invention relates generally to tubular shafts manufactured from composite materials and, more particularly, to composite shafts for golf clubs and other articles.
2. Description of the Related Art
Recently, substantial attention has been directed toward the development of lightweight tubular shafts for golf clubs and other articles such as fishing rods. Such shafts are commonly manufactured from sheets of composite materials, including, for example, various forms of xe2x80x9cpre-preg.xe2x80x9d Pre-preg composite sheets are formed by pulling strands of fiber, for example, carbon or glass fiber, through a resin solution and allowing the resin to partially cure. Exemplary resins or xe2x80x9cbinding matricesxe2x80x9d may include, for example, thermoset epoxy resins and thermoplastic resins. Alternatively, pre-preg sheets may be manufactured by pulling a fabric or weave of composite fiber through a resin solution and allowing the resin to partially cure. In either case, once the resin is partially cured or xe2x80x9cstaged,xe2x80x9d the resin holds the fibers together such that the fibers form a malleable sheet
When using pre-preg sheets, shafts generally may be manufactured by wrapping a set of plies of pre-preg composite sheet around a mandrel in a predetermined manner, wrapping the ply-wrapped mandrel in a binding material such as cellophane or polypropylene tape, and heating the ply-wrapped mandrel to a predetermined temperature for a time sufficient to allow the resin in the pre-preg composite sheets to become fully cured. Once the resin has been fully cured, the binding material may be removed from the exterior of the shaft, and the mandrel may be removed from the core of the shaft.
Alternatively, a set of plies of pre-preg composite sheet may be wrapped around a bladder covered mandrel, and placed in a mold. If desired, the mandrel may be removed leaving the bladder and plies in the mold, or the mandrel may be left in the mold. In either case, the bladder may be inflated to a predetermined pressure to force the plies of pre-preg against the walls of the mold, and the mold may be heated to a predetermined temperature for a time sufficient to allow the resin in the pre-preg composite sheets to completely cure. Once the resin has been cured, the cured plies (shaft) and mandrel may be removed from the mold, and the bladder (and mandrel if not previously removed) may be removed from the shaft. The resulting shaft may then be used to manufacture such articles as golf clubs and fishing poles.
When assembling golf clubs or fishing poles, a handle or grip, made from rubber, leather, cork or similar materials, generally will be placed on one end of the shaft. Such grips generally provide a tacky or slip-resistant surface which enables a person to securely grasp the golf club or fishing rod and minimizes the likelihood that the golf club or fishing rod will slip out of or change position within the person""s hands during use.
Often, the grip provided may comprise a substantially cylindrical sleeve having an open end and a substantially closed end. The sleeve is introduced over the end of the shaft and extends longitudinally over a portion of the shaft such that the closed end of the grip engages the end of the shaft. The grip generally may be fixed on the shaft by friction and/or through the use of conventional adhesives or adhesive tapes.
Alternatively, a wrapped tape grip may be used. Rubber or similar tape material, commercially available in rolls and possibly having a backing adhesive, may be helically wound over the end of a shaft. Then, a cap may be placed over the end of the shaft, holding the end of the tape and keeping it from potentially unwinding.
Conventional grips, however, may add substantial and undesired weight to the shaft overall, or may add weight in a location that is not optimal for the design of a particular article. For example, in the case of golf clubs it is sometimes a goal to substantially reduce the overall weight of a shaft, or to move weight from an end of the shaft to another location. Weight reduction or weight shifting in a golf club shaft is limited, however, by the need to provide a grip on the end of the shaft, with traditional grips adding between about 45-50 grams to the weight of the shaft, and ultra-light grips adding about 20 grams.
Accordingly, it is believed that those in the field of golf club design would find a substantially reduced weight grip that is both durable and economical to manufacture to be quite useful. It is also believed that methods of forming a reduced weight grip on the end of a shaft for a golf club would be found to be useful.
The present invention is directed to improved shaft grip structures for use with golf clubs, fishing rods, and other articles of manufacture. In one innovative aspect, a grip formed from composite materials forms an integral grip portion of a proximal region of a shaft. If desired, the grip may have a predetermined geometry and/or an ornamental pattern formed thereon.
To manufacture a shaft with an integral grip in accordance with the present invention, a first set of plies of pre-preg composite sheet is selected and used to form the overall body of a shaft. Another set of plies of pre-preg may be selected to be included in the grip region of the shaft. For example, lower modulus, toughened plies may be used to form the integral grip portion of the shaft. This may result in the provision of a softer cured material for the grip which creates a more comfortable, rubber-like feel.
A resin film, possibly including reinforcing fibers, also may be added to the grip region. Films using Inter Penetrating Networks (IPNs) or similar resins, such as rubber, urethane, or epoxy films, may be used in the grip region so that the resulting grip has a soft, yet tacky, feel when cured. Most preferably, a resin film of ethylene propylene diene monomer (EPDM) copolymer is applied to the first set of plies of pre-preg and co-molded using the process described below.
Once the materials comprising the shaft have been selected, a molding process may be used to form the shaft. The molding process preferably includes a single curing step in which the composite materials of the overall shaft body and the composite materials and/or resin film of the grip are simultaneously shaped and cured. Stated differently, the composite materials of the shaft body and those of the grip are co-molded or co-cured. For such a molding process, a conventional mandrel having predefined dimensions is selected and covered by a latex sheath or bladder. Plies of pre-preg composite sheet and resin film may be wound around the mandrel in a predetermined manner, and the wrapped mandrel may be placed in a mold. The mold generally will include a cavity having a predefined shape for the shaft and grip region, and the shape of the cavity corresponding to the grip region may be shaped for applying a predetermined grip geometry and/or ornamental design to the grip region of the shaft.
If desired, the mandrel may be removed, leaving the sheath and surrounding plies in the mold. Alternatively, the mandrel may remain in the mold during the curing process. Pressurized gas may then be introduced to inflate the bladder and force the plies of pre-preg and resin film against the wall of the mold. The mold may then be heated for a selected period of time, that is, a time sufficient to allow proper curing of the resin comprising the various plies. Thereafter, the shaft may be removed from the mold, and the latex sheath (and mandrel if not already removed) may be removed from the core of the shaft.
The cured composite material and co-molded resin film may provide a substantially finished surface for the shaft, although preferably the grip region will be coated using a light coating material, such as Durasoft manufactured by Akzo Nobel of Troy, Mich., which may provide additional comfort, vibration dampening and/or slip resistance. Preferably, in addition to having a resin matrix film co-molded with the shaft, the grip region of the shaft body may be coated typically by dipping or spraying the coating onto the surface of the grip.
While conventional grips for golf clubs weigh on average between about 20 and 50 grams, the integrally molded grip of the present invention may reduce this weight to less than about 5-8 grams. Thus, where conventional composite golf clubs may weigh about 300 grams, similar clubs including a shaft in accordance with the present invention may achieve weights as light as approximately 255 grams. Alternatively, using a grip in accordance with the present invention it may be possible to redistribute as much as 45 grams of mass within the length of a conventional composite golf club shaft. Somewhat smaller, though still significant, reductions or redistributions of mass (on the order of 15 grams) may be achieved in the case of ultra-light shafts.
Accordingly, a principal object of the present invention is to provide a shaft for a golf club, a fishing rod or other article of manufacture that has a grip directly molded thereon, eliminating the need for conventional grips, and to provide methods of manufacturing such shafts.
It is also an object of the present invention to provide a golf club shaft having a substantially reduced weight relative to golf club shafts using conventional grips.
It is still another object of the present invention to provide a means for reducing the mass associated with a grip for a golf club shaft and for distributing additional mass within the length of the golf club shaft.
It is a further object of the present invention to provide a shaft that includes an integrally molded grip that substantially reduces the likelihood that the grip will separate from the shaft during the life of a golf club.
It is an additional object of the present invention to provide a golf club shaft having a desired grip geometry, optionally including an ornamental design, molded directly onto the shaft itself, and to provide methods of manufacturing such shafts.
Having briefly described the present invention, the above and further objects, features and advantages thereof will be recognized by those skilled in the pertinent art from the following detailed description of the invention when taken in conjunction with the accompanying drawings.